Gun system for cathode ray tubes



Aug. 6, 1957 w. BERTHOLD 2,802,139

GUN SYSTEM FOR CATHODE RAY TUBES Filed May 19, 1954 Direction of the electrical field Potential lines Electron lens Screen Fig. 3

lNVENTOR T w. BERTHOLD ATTQR United States Patent Qflfice 2,802,139 Patented Aug. 6, 1957 GUN SYSTEM FOR CATHODE. RAY TUBES Wolfgang Berth-old, Stuttgart-Weilimdorf, Germany, as-

signor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application May 19, 1954, Serial No. 430,927 Claims priority, application Germany May 30, 1953 4 Claims. (Cl. 315-13) This invention relates to gun systems for cathode ray tubes, particularly television tubes.

The clarity of a picture produced by a television tube is necessarily the result of a compromise between the resolution in the horizontal and vertical direction, and the visibility of the scanning lines. In the direction of the lines the definition is poorer because of insufficient focus of the picture points which insufficiency is increased by the limited bandwidth transmitted.

In order to avoid this difliculty and achieve a given definition in the line direction, it has been suggested heretofore to design the apparatus so that the focused spot appears on the fluorescent screen in elliptical shape. This effect has been achieved for instance by the aid of magnetic coils which astigmatically distort the electron stream. This method has however produced poor results because the shape in the direction vertically of the line is somewhat deformed or blurred. The reason for this is that the focusing of the elliptical point with a variation in intensity follows a bell-shaped curve (similar to a Gauss error distribution curve, meeting the requirements of the equation and the resulting elliptical point deviates considerably from the ideal shape which would be of a rectangular cross-section. Better results have been obtained by employing the method known as line wobbling in which the electron beam under the control of a high frequency (greater than me.) is deflected or wobbled slightly vertically of the line so that the sharp point will be changed to a small or narrow band of the desired width. The above method however requires a generator for producing the high frequency.

In accordance with the present invention, for reducing the visibility of the line structure without creating the above-mentioned deficiencies, a gun system is employed of the kind in which one or more beams of an electron source are divided into two or more beams. These beams are subsequently assembled with the aid of conventional collecting devices on the fluorescent screen either completely or nearly completely at one or more focusing points or spots, the splitting and the collection of at least two beams being performed in such a way that the focal points of these beams are arranged vertically with respect to the direction of the line, one above the other. By variation of the spacing of the points it will then be possible to produce the necessary width of the line. The dividing of an electron beam into two or more separate beams which are separately controlled and deflected is already known, having been employed with the so-called multi-beam oscillographs. There the problem is to record several processes on the screen of the cathode ray oscilloscope tube at the same time. The present invention, however, aims to permit production on the fluorescent screen of a focused spot with a predetermined shape.

The division of the beam can be performed, for example, by electrostatic means arranged to affect different parts of the beam in different ways through transverse electric fields. For instance it is possible to divide the beam by means of a narrow electrode, to conduct it through separate deflecting fields and to focus it finally by means of a common focusing coil to produce the two points on the fluorescent screen. This may be achieved in a simple way by a wire conductor mounted on an insulating support and positioned in the anode space, this wire being connected by way of a resistor (e. g. photoresistor) or a gas discharge gap with the anode. With the aid of the photoresistor the size of spreading of the picture spots can be varied by external exposure. It will be of some advantage to arrange this insulated wire in such manner that the electron beam is divided as exactly as possible into two halves. As a result of the electrons striking the wire there will flow in the latter, according to the secondary emission coefiicient of the metal, either a positive or a negative current whereby the potential of the wire will be changed. 'It is also possible to use the secondary emission coefficient 1 for setting a proper deflecting field strength. A suitable design of the surrounding anode components will produce for both of the beam halves opposite deflecting fields.

It is advantageous to perform the beam splitting or division where the beam has a large cross-section because then the electrode will not take up so much current and no great precision will be required for the accuracy of the arrangement of the wire.

By the employment of asymmetrical deflecting fields the two points may be positioned one below the other which will be of some importance when the cross-section of the points is small and the space between the points great. In such cases it will be unnecessary to split the beam into three or more points.

In the drawings,

Fig. 1 shows schematically in end elevation and Fig. 2 in side elevation an embodiment of the invention; and

Fig 3 shows the ray path in an exemplified embodiment according to the invention.

Referring more particularly to the figures, reference numeral 1 indicates the anode of a gun system which is partially shown. Reference numeral 2 indicates the anode diaphragm and 3 the neck of the tube in which the anode is arranged. Reference numeral 4 indicates a thin wire, e. g. of tungsten, which is insulatingly suspended at a short distance in front of the anode diaphragm.

The potential lines which are formed between the wire and the cylinder of the anode are denoted by dash lines. The direction of the electric field (indicated by the arrow) is opposite on one side of the wire to that on the other side of the wire. The wire is connected with the anode through the resistor 5. In the case of electrostatically focused picture tubes the direction of the wire corresponds to the direction of the scanning line, whereas in the case of magnetically focused tubes it is rotated by approximately 60 from this direction.

In Fig. 3 reference numeral 1 denotes the anode, 2 the anode diaphragm, and 3 the neck of the tube. In the control electrode 6 there is arranged the cathode 9. The electron beam which is produced by the cathode 9 is split into two beams and is spread by the electrode 4. By means of the electron lens or lens system either (magnetic or electrostatic) the thus divided beams will be made visible on the screen 8 in the shape of two spots separated from each other.

While I have described a particular embodiment of my invention for purposes of illustration, it should be under stood that various modifications and adaptations may be made within the spirit of the invention as set forth in the appended claims.

What is claimed is:

1. A gun system for cathode ray picture tubes having a fluorescent screen and means for scanning the electron beam over the surface of said screen in line and frame scanning relation, comprising an electron source for producing an electron beam, means for splitting said beam in at least two beams, and means for focusing said beams on said screen in overlapping relation spaced perpendicularly to the line scanning direction of beam movement, said means-for-providing-an-electric-field comprising an insulating electrode transversely mounted with respect to said electron beam and further comprising means for producing an electric field transverse to said beam to accelerate said two beams in different directions under control of the potential on said electrode.

2. A gun system according to claim 1, further comprising an electron gun anode and a resistor coupling said electrode to said anode to develop said potential.

3. A gun system according to claim 1, wherein said electrode is made of secondary emissive material said potential being developed by secondary emission caused by impact of said beam on said electrode.

4. A gun system according to claim 1, wherein said means for splitting said beam is positioned in the region of largest cross section of said electron beam.

References Cited in the file of this patent UNITED STATES PATENTS 

